Recently, problems of air pollution due to the exhaust gas especially from automobiles have become serious, and the need for catalyzers for purification of air has become more severe. To this end, changes in catalyzers are being intended from those using ceramic carriers heretofore used to those using metallic carriers which have far superior purification characteristics. As the material for the metallic carriers, there are ferritic heat-resisting stainless steels including aluminum based stainless steel of 20 wt % Fe and 5 wt % Cr etc.
The plates made of such a heat-resisting stainless steel is generally formed in honeycomb structure and is used in the exhaust gas systems of an engine. However, the catalyzers using the metallic carriers are not activated when they are in a cooled state, i.e. in the so-called "cold start", so that sufficient purifying action can not be achieved.
As measures for enhancing the efficiency of the catalyzer in the cold start, there have been proposed means for preheating the catalyzer by flowing the electric current through the metallic carrier thereof so as to start the engine under the condition in which the activation of the catalyzer is raised, and means for forming novel honeycomb structure in which the plane plate portion are formed in a finely corrugated shape or the plane plates are replaced solely by corrugated plates so that the rising speed of the temperature of the catalyzer caused by the exhaust gas is accelerated to thereby shorten the time required for activation of the catalyzer.
However, in the former case in which the catalyzer is preheated, the electric power consumed thereby is very great such as 4.5-5 kw in the case of the catalyzer of small size passenger vehicle even though sufficient purification action is achieved. Therefore, it becomes necessary to prepare a separate battery for preheating the catalyzer, which means the retrogradation to the weight reduction of the automobile. Further, in the later case in which the honeycomb structure is modified, it is insufficient to meet, for example, the final value set in the regulation (quantity of exhaust of HC per 1 mile traveling controlled to max. 0075 g) enacted in California, U.S.A. in October 1990.